JPS59216114A - Retrofocus type wide-angle lens - Google Patents

Abstract

PURPOSE:To reduce aberration deterioration due to focusing by allowing a lens system consisting of a divergent front group and a convergent rear group to meet specific requirements. CONSTITUTION:The front group F1 consists of two negative meniscus lenses L1 and L2 having convex surfaces at object field sides, a positive lens L4 at an image field end, at least one convex lens L5 at an object field side about the stop S in the rear group F2, and a biconcave lens L7 at an image field side about the stop S and two convex positive meniscus lenses L8 and L9 at the image field side successively from the object field side. The conditions shown by inequalities I -V are satisfied. In the inequalities, (f) is the focal length of the whole system in the infinite-distance state, and f1 and f2 are the focal lengths of the front group F1 and F2; and f12 is the focal length of the positive lens L4 in the front group F1 at the image field end and f21 is the focal length of the lens group in the rear group F2 on the object field side about the stop S.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a retrofocus wide-angle lens for a single-lens reflex camera that focuses by extending a part of the lens system.

- A wide-angle lens for an eye reflex camera requires a back focus of a certain length or more, and generally a retrofocus wide-angle lens with a divergent group at the front and a convergent group at the rear is used. The focusing is normally performed by extending the entire lens system. However, in the focusing method in which the entire lens system is extended, the moving lens becomes heavy and large.

Therefore, for an autofocus lens that is required to perform focusing with a small driving force, it is desired to achieve focusing by moving a part of the lens system.

Lens systems of this kind have been proposed in the past, but they generally have the drawbacks of being large in size, having a complicated focusing structure, and causing large fluctuations in aberrations due to focusing.

An object of the present invention is to eliminate the drawbacks of the conventional examples described above, and to provide a retrofocus wide-angle lens that has a simple focusing structure, has little deterioration of aberrations due to focusing, and is suitable for compact autofocus photography lenses. It is about providing.

The structure of the first embodiment of the present invention to achieve the above object is composed of a divergent front group F1 and a convergent rear group F2, as shown in FIGS. 1(a) and 1(b). In the retrofocus type wide-angle lens, the front group F1 includes at least two negative meniscus lenses L1.
A positive lens L4 is provided at the end of F2 and the image field side, and at least one biconvex lens L8 is provided closer to the object world than the aperture S existing in the rear group F2, and in order from the object world side to the image field side of the aperture S,
It has at least a biconcave lens L7 and two positive meniscus lenses L8 and F8 with convex surfaces on the image field side, where f is the focal length of the entire system at infinity, and fl is the front group F.
1 focal length, f2 is the focal length of the rear group F2, F12 is the focal length of the positive lens L4 at the image field side end of the front group F2, F21
is the lens group L5 located closer to the object world than the aperture S in the rear group F2.
, when the focal length is F6, (1) 0.5f<Ifl
l<0.9f (2) 0, 3< f12/1fll (3) 0.8<
f2<1.3f (4) 0,03<F21/f2(1)~(4)
The following conditions are simultaneously satisfied, and focusing is performed by changing the lens distance between the front group Fl and the rear group F2.

The front group F1 includes two negative meniscus lenses L1. It is preferable to have F2, a negative lens L3, and a biconvex positive lens L4 at the end on the image field side.

As shown in Fig. 1(a) and (b), the front group F1 is composed of negative lens groups L1, F2, F3 and positive lens J+$L4 from the object side, and the pack focus of the front group F1 is lengthened. However, it is possible to make the focal length of the front group F1 relatively large. This reduces the divergence of the axial rays between the front group F1 and the rear group F2, reduces the fluctuation in the height of incidence of the axial rays on the rear group F2 when focusing starts in the rear group F2, and reduces spherical aberration. fluctuations are reduced.

Regarding the rear group F2, in order to be able to correct small aberration fluctuations due to focusing, from the object world side, positive lens groups L5 and F6, negative lens group L7, and positive lens li'4
It consists of three groups: 1, 13, and F8. Furthermore, a diaphragm S is provided between the positive lens L6 and the negative lens L7 on the object world side, so that the position through which the off-axis rays pass due to focusing does not vary greatly, thereby reducing fluctuations in off-axis aberrations. I can do it.

To explain the conditions of the present invention in more detail, condition (1) weakens the refractive power of the front group Fl, weakens the divergence of the axial rays between the front group F1 and the rear group F2, and
This is the condition for correcting the fluctuation of the spherical aberration in No. 2 to a small value. If the lower limit of this condition (1) is exceeded, fluctuations in spherical aberration due to focusing will increase, and if the lower limit is exceeded, the pack focus will become short and hard, and the diameter of the front lens will become large, which is undesirable.

Further, condition (2) is a condition for determining the refractive power of the positive lens group constituting the front 1\F1 under condition (1). If this lower limit value is exceeded, aberrations will increase in the front group F1, and if this upper limit value is exceeded, sufficient hack focus will not be obtained.

Furthermore, condition (3) is a condition for determining the refractive power of the rear group F2 based on condition (1). If the lower limit is exceeded, the refractive power of the rear group F2 will become too strong, making it difficult to correct aberration fluctuations due to focusing of the rear group F2, and if the upper limit is exceeded, the focusing movement will become large and the entire lens system will becomes larger.

Condition (4) is a condition for determining the refractive power of the positive lens groups L5 and F6 on the object world side from the aperture S in the rear group F2 under condition (2). If the lower limit of is exceeded, the variation in spherical aberration due to focusing becomes large, and if the upper limit is exceeded, the variation in off-axis aberration becomes large.

Next, a numerical example of a lens configuration and an aberration coefficient table will be described for a first example that satisfies each of the above-mentioned conditions. In the numerical example of the lens configuration, Ri is the radius of curvature of the first lens surface according to the order of light progression, dl is the axial thickness of the first lens or the distance between lenses, and Ni and ν1 are the respective values of the first lens. These are the glass refractive index and Abbe number for the d-line. In addition, in the table of aberration coefficients, the surface number is the lens surface counted according to the direction of light travel, ■ is the spherical aberration coefficient, ■ is the coma aberration coefficient, ■ is the aberration coefficient, P is the Petzval sum 1, and ■ is the distortion aberration coefficient. It is.

Example 1 f=100. OFNO=1:2.8
2ω=74.2f 1=-1!39.00
f12=148.288f2=105.4
1 f12= 76.847β=-0
,0? When focusing on the rear group, D8 = 13.95 Aberration coefficient of Example 1 RNOI II [I PV
l 0.11+4 0.0881 0.0B8
? 0.3209 0.30!312 -3.5
378 0.0040 -0.0000 -0.67
24 0.00083 0.2801 0.238
3 0.2045 0.0814 0.24434
-5.2220 -0.4903 -0.0480
-0.4041 -0.04235 0.8236
0.5017 0.305B -0,0B55
0.1462B -2,101f (-0,747B
-0,2859-0,0187-0,10127[
1,19710,89490,12920,28170
,05938-0,00f30 -0.032f(-0
,17800,1183-0,325991,6040
' 0.7200 0.3232 0.2917
0.27e010 0.1976 -0.227
8 0.2[1210,0791-0,392911
-0,0183-0,0288-0,04490,27
410,3594123,4θ5? -1,6407
0,77010,1059-0,4112130,00
,00,00,00,0 +4 -10.4387 2.8908 -0.80
013 -0.469I O,351615-2,
1388-1,453t (-0,9888-0,401
8-0,9458180,0029-0,02260,
179!3 -0.24f31 0.52851?
1.0101 -0.3125 0.0967
0.5058 -0.186418 -0.0434
0.0574 -0.0780 -0.1717
0.327El.

19 10.9811 -0.0780 '0.00
06 0. f(020-0,0043Σ 1.19
91 0.3f121 -0.0585 0.21
17 0.1!308 Fig. 2 is an aberration diagram of the first embodiment when the object distance is infinite, and Fig. 3 is an aberration diagram when the object distance is infinite in the first embodiment. It is an aberration diagram when focusing, and it is a close-range IJF
It can be seen that the aberration fluctuations are small even when focusing on . Furthermore, FIG. 4 shows, for reference, that the lens system of the Ml embodiment is extended to its entirety, and the imaging magnification β=-0,0.
Regarding the aberration li+ when focusing at 7, it can be seen that the aberration variation in this case is rather smaller than in the normal overall focusing.

FIG. 5 is a lens configuration diagram of the second embodiment, in which the two positive lens groups L5 and F of the rear group F2 are compared with the embodiment of FIG.
6 is one positive lens L5. Numerical examples and an aberration coefficient table of a lens configuration that satisfies each of the above-mentioned conditions in this second embodiment will be described next.

Example 2 f=looo, OFNO=1:2.8 2
ω=74.2fl=-212, 13f12=1 :4.
283f2= 103.32 f21-7
4.594/3 = -0,07 rear group 7 Au Cuff, (
7) Toki, D8=14.01 Aberration coefficient of Example 2 RNOI II Ill P
Vl 0.1f349 0.1029
0.0842 0.31358 0.2682
2 -3.2820 0.0032 -0.0000
-0.13853 0.000?3 0.347
5 0.2578 0.1909 0.1399
0.24524 -4.2[104-0,5721
-0,0768-0,4148-0,086050,3
4130,335? 0.3303 -0.115
2 0.211f (6~3.8520 -0.91f
iO-0,2297-0,10430,083878,
88830, 89800, 144fl O, 275
50,08098-0,00380,0229-0,1
38130,2030-0,38!159 4.74
13 1.3727 0.3974 0.552
3 0.275010 5.5239 -2.20
94 0.8837 0.2190 -0.441
011 0.0 0.0 0.0 0.
0 0.0+2 -11.8591 3.122
7 -0.8364 0.5287 0.3859
13 -2.5246 -1. [1741-1,110
1-0,4170-1,0128140,01220,
060? 0.3025 -0.1773 0.8
23215 1.5328 -0.4041 0.
10613 0.5344 -0.1139016
-0.0418 0.0658 -0.1035 -
0.1121 0.339417 7.6235-
0.4038 0.0214 0.5069 -0
．． 0280Σ 1.7498 0.1830 -0
．． 0537 0.2411 0.20 (1' Fig. 6 is an aberration diagram of the second embodiment shown in Fig. 5 when the object is at infinity. Fig. 7 shows the aberration diagram when the object is at infinity in the second embodiment shown in Fig. 5. In this case, the imaging magnification β = -0.07 This is an aberration diagram when focusing, and it can be seen that aberration fluctuations due to focusing are small in this example as well.

In this way, the retrofocus type wide-angle lens according to the present invention performs focusing by moving a part of the lens system, so the weight of the focusing lens is small, and the focusing structure is simple because only the rear group of the lens system is moved. You will be able to do it. Therefore, this lens system is extremely suitable as a trofocus type wide-angle lens for automatic focusing that requires focusing with a small driving force.

Furthermore, since there is little variation in aberrations due to focusing, a lens system with excellent performance at all shooting distances can be obtained.

[Brief explanation of the drawing]

FIG. 1(a) is a lens configuration diagram of the first embodiment of the retrofocus wide-angle lens according to the present invention in a state at infinity photography, and FIG. 1(b) is a lens configuration diagram of the rear group of the first embodiment. Fig. 2 is an aberration diagram of the first embodiment when shooting at infinity, and Fig. 3 is the rear group of the first embodiment. FIG. 4 is an aberration diagram when the imaging magnification due to focusing is β=-0,07, and FIG.
07, FIG. 5 is a lens configuration diagram of the second embodiment when shooting at infinity, FIG. 6 is an aberration diagram of the second embodiment when shooting at infinity, and FIG. 7 is an aberration diagram of the second embodiment when shooting at infinity. FIG. 7 is an aberration diagram in a state where the photographing magnification is β=−0.07 due to focusing of the rear group in the second embodiment. In the drawing, Li is the first lens according to the order of light progression, Ri is the radius of curvature of the first lens surface, di is the axial thickness or distance between lenses, Li is the lens, S is the sagittal focal line, m
is the meridional focal line. Patent applicant Canon Co., Ltd. No. 4 No. 3 F2.8 378 37°

Claims (1)

[Scope of Claims] 1. A retrofocus wide-angle lens consisting of a diverging front group and a convergent rear group, in which the front group includes at least two negative meniscus lenses having a convex surface on the object side, and an image field. A positive lens is provided at the side end, and at least one biconvex lens is provided on the object world side of the aperture located in the rear group, and at least one biconvex lens and a convex surface on the image field side are provided in order from the object world side to the image field side of the aperture. It has two positive meniscus lenses, where f is the focal pressure of the entire system at infinity, N[, fl is the focal length of the front group, f2 is the focal length of the rear group, and fl2 is the image field side edge of the front group. When the focal length of the positive lens, f21, is the focal length of the lens group on the object world side from the aperture in the rear group, (1) 0.5f<Ifll<0.9f (2) 0, 3< f12/l fil <1,
0(3) 0, 8 f<f2<1, 3f(4)
0, 03<f21/f2<0, 13(1)~
A retrofocus wide-angle lens that simultaneously satisfies each of the conditions (4) and performs focusing by changing the lens distance between the front group and the rear group. 2. The front group includes two negative meniscus lenses and a negative lens having a convex surface on the object world side, and a biconvex positive lens on the image field side end,
At least one diaphragm exists on the object world side of the aperture in the rear group.
Claim 1 having two double-convex lenses
Retrofocus wide-angle lens described in section.